The objective of this work is to develop quantitative measures from chest radiographs to detect circulatory failure at its early stages. Envisaged for eventual clinical use the work plans to perform a prospective study of monkeys to develop the necessary measures. Chest radiographs taken at various stages of induced circulatory failure will be analyzed using optical processing techniques combined with on-line computer data handling. The measures thus derived will be correlated with physiological indices recorded concurrently thereby demonstrating their validity to correctly assess the true state of early cardiac failure by a non-invasive technique.